JPH095026A - Photoelectric position measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric position measuring device using a well- known scanning principle, which generates the signal on the basis of an interference of a light beam diffracted by a grid scale and of which structure is simplified and which can be manufactured at a low cost. SOLUTION: Light of a light source L is modulated in response to the position by plural grids 1, 2 having a constant scale cycle and to be moved in relation to each other in the measuring direction X, and the light beams to be deflected by at least one grid are interfered with each other, and plural light detecting unit D0 , D1 , D2 for detecting the dependent signal are provided at positions, of which the phase is displaced from each other, are provided. At least one grid 1 is arranged in order in the measuring direction X among each scale period (d) directed to the measuring direction X, and has at least three areas B1 , B2 , B3 vertically extended in the measuring direction X, and each area B1 , B2 , B3 has the light selective characteristic different from each other, and each signal beam obtained from these areas B1 , B2 , B3 enter a corresponding light detecting units D0 , D1 , D2 , and these light detecting units are arranged in the lateral direction in relation to the measuring direction X.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source which is caused by such gratings when light beams diffracted by the gratings interfere with each other and a plurality of photodetectors detect a phase shift interference signal. Relates to a photoelectric position-measuring device in which the light is modulated according to the position.

[0002]

2. Description of the Related Art A position measuring device of this kind is disclosed, for example, in EP 0 163 262 B1. In that case, the reflective scale grating is arranged so as to be movable relative to the scanning grating. This scanning grating is
In order to generate an electrical signal that is 120 ° out of phase, it is formed as a phase grating with a constant ratio of web to groove. A group of co-directed diffracted beams is focused on each of the three detectors that are placed downstream. In these military diffracted beams pointing in the same direction, it is also called the so-called obtained diffraction order. The resulting diffracted beam of n diffraction orders is a group of beams generated from the whole system of both diffraction gratings in the same direction as if it were deflected by only one diffraction grating to the n diffraction order, ignoring the reflection on the scale plate. Equivalent to.

The scanning grating used is optically designed or dimensioned so that the different diffraction orders correspond to the signals of the desired phase difference. To ensure that the different signal components are spatially separated at the detector side, the imaging optics provided must have a certain minimum focal length between the scanning grating and the detector. The focal length of the focusing lens is about 30 mm in a measuring system of this kind with a wavelength of 880 nm and a graduation period T = 20 μm. this is,
The scan head structure is made quite large.

Since the minimum focal length of the optical system described is approximately proportional to the scale period of the scale or grating used,
This presents a structural size problem, especially when it is desired to scan a graduation plate with a coarse graduation period on the basis of this measuring principle.
German Patent 34 16 864 C2 discloses a position-measuring device with a lateral scale, in which a scanning plate with a diaphragm structure scans the scale plate. In the case of this position-measuring device, the lateral scale is composed of a number of strip-shaped diffractive elements which are arranged adjacent to each other in the measuring direction and have a grating web extending parallel to the measuring direction. Since the individual diffractive elements differ with respect to their lateral period, they cause the generated light beam to be deflected in different directions. When this lateral scale is illuminated through the gap in the scanning plate, a deflected light beam bundle is produced, each deflection of which depends on the lateral scale period and the illuminated lateral grating area. Thereby, the position of the scale plate can be guided. The light beam bundles deflected in different directions pass through a lens and are focused on various photodetectors in the focal plane of the lens.

The position-dependently modulated signal is generated on the basis of the moire principle in this known position measuring device. That is, the evaluation of the interfering partial beam bundles is not used for position measurement. In the known position-measuring device of EP 0 220 757 B1 as well, the graduation plate has an area with lateral graduations arranged in sequence in the measuring direction and a reflective or transmissive area. The lateral scale region is configured as a phase grating, the grating parameters of which are chosen so that the zero diffraction orders that occur are eliminated and all other diffraction orders do not enter the photodetector.
Areas with a lateral scale are considered areas that are not reflected or transmitted by the photodetectors and do not act as direction selectivity with respect to the multiple photodetectors.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a photoelectric position measuring device which is simple to form and which can be manufactured in a cost-effective manner. In that case, it should be possible to use the scanning principle known, for example, from EP 0 163 362 B1. That is, signal generation is based on the interference of light beam bundles diffracted by one or more grating scales. In that case, it is also necessary to make the structure of the scanning head compact and to scan a particularly coarse graduation period.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the above-mentioned problem is caused by the fact that a plurality of gratings 1 and 2 having a constant scale period and moving relative to each other in the measuring direction X cause the light of a light source L to be positioned. A plurality of photodetectors D _0, D _1, D ₂ for detecting the signals depending on the positions where the light beam bundles that are modulated in accordance with each other and are diffracted by at least one grating interfere with each other and are out of phase with each other, and at least At least three regions B _{1 and} B 1 in which one grating 1 is sequentially arranged in the measuring direction X and extends substantially perpendicular to the measuring direction X in each of the graduation periods d facing the measuring direction X.
_2, B ₃ , each of these regions B _1, B _2, B ₃ having different light-selective properties, the signal beam obtained from these regions B _1, B _2, B ₃ Photodetectors D _0, D with each bundle attached
This is solved by a photoelectric position measuring device which is incident on _1, D ₂ and whose photodetectors are arranged substantially transverse to the measuring direction X.

[0008] Other advantageous configurations according to the invention are set out in the dependent claims.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings. The basic functional principle of the position measuring device according to the present invention will first be briefly described with reference to FIG. The corresponding optical diagram is shown in FIG. In this case, the light from the light source is collimated via the collimator lens K and is incident on the phase grating 1 having a constant scale period d. In the position measuring device according to the invention, when the graduation grating 2 and the scanning grating 1 move relative to each other in the measuring direction X, the first grating 1 is special because it generates scanning signals depending on a number of phase shift positions. It is formed as a scanning grating 1 having a lateral pattern. FIG. 3 shows a scanning grating 1 according to the invention. FIG. 4 shows an enlarged portion of the scanning grating 1 of FIG. In the case of the exemplary embodiment shown, this scanning grating 1 has partially laterally patterned regions B _1, B _2, B ₃ which are connected periodically in the measuring direction X. Areas B _{1 and} B viewed in the measurement direction X
_2, B ₃ have almost equal widths. The sum of the widths of the first, second and third areas B _1, B _2, B ₃ corresponds to the graduation period d of the scanning grating. This graduation period is the same as the graduation period c of the graduation grating 2, but it does not necessarily have to be the same. Each area B _1, B
The width of _2, B ₃ is d / 3 in this example.

The second and third areas B _2, B ₃ are in the measuring direction X
With respect to the lateral direction, these gratings have different lateral lattice constants d ₂ and d ₃ in the Y direction. In this case, the scale lines of the individual gratings are oriented parallel to the measuring direction X. Lateral regions B _2, which is formed as a blazed phase grating B ₃ further or incident beam bundle is set to deflect the respective +1 diffraction order, or optimized. As schematically shown in FIG. 5, when a collimated light beam bundle is incident on the scanning grating 1, regions B _{2 and} B ₃ having different patterns in the lateral direction make the incident light beam bundle substantially in each region B ₂ or B. included with ₃ +
Deflection to one transverse diffraction order b ₂ or b ₃ . Area B _2, B ₃
Due to the variously selected grating parameters at 1, the diffracted partial beam bundle is deflected to another angle. Therefore, the areas B _2, B
₃ has different directional selectivity with respect to the diffracted partial beam bundle depending on the lattice constants d _{2 and} d ₃ .

On the detector side, three detectors D _0, D ₁ and D ₂ formed as optoelectronic elements are provided. These detectors are arranged transverse to the measuring direction X, i.e. in the Y direction. Each of the detectors has three regions B _1, B
It is attached to one of _the B _{2 and} B ₃ and is arranged in the Y direction so that each detector is activated only by the signal component coming from the area to which it is attached.

The first region B ₁ is made transparent in the illustrated embodiment of the position measuring device according to the invention. That is, the region B ₁ makes the passing light beam bundle b ₁ incident on the graduation grating 2 without diffracting, the light beam bundle b ₁ is reflected from the graduation grating in accordance with the incident angle, and passes through the grating 1 again. . Since the other two regions B _{2 and} B ₃ are configured to have direction selectivity, that is, since the deflection is performed in the +1 diffraction order, the region B ₁ also has direction selectivity to these regions. Become.

[0014] When the light beams b ₁ reflected from the scale grating 2 which passes through the area B ₁ of the scanning grating 1 the second time, since no diffraction laterally 0 diffraction order b ₁ obtained the light beam bundle Is regarded as pseudo. The light component of the light beam bundle b _{1 which} is laterally deflected from the regions B ₂ and B ₃ when passing the scanning grating 1 a second time contributes to the 0 diffraction order b ₁ ′ obtained and detected accordingly. do not do.

The scanning grating 1 acts like an amplitude grating in the direction of the 0th lateral diffraction order. The light component recorded in the direction of the 0th lateral diffraction order passes only the region B ₁ ,
It does not pass through the patterned areas B _2, B ₃ of the scanning grating 1. This scanning pattern therefore appears in the detection direction as an amplitude scale with periodic arrangement of transparent areas B ₁ and opaque areas B _2, B ₃ .

Considering the beam bundle in the region B ₂ which exits when the region B ₁ of the scanning grating 1 is first passed and is deflected in the direction of the +1 diffraction order when passing the scanning grating 1 the second time,
The signal components from the regions B ₂ and B ₃ cannot be obtained in the direction of b ₂ '. Only the light from region B ₂ is captured by the corresponding detector D ₁ . Therefore, this scanning pattern looks like an amplitude scale in which the opaque area B _{1, the} transparent area B _{2, and the} opaque area B ₃ are periodically arranged in the detection direction.

Area B of the scanning grating 1₁When you first pass
When exiting and passing the scanning grid 1 for the second time
Area B deflected in the direction of the direction diffraction order_ThreeConsider the beam bundle of
If you think about it, b_ThreeArea B in the direction of '₁And B₂From the signal component
Not obtained, corresponding detector D ₂Area B_ThreeLight from
Only detected. Therefore, this scanning pattern is
Opaque area B toward₁And B₂And transparent area B_ThreeThe periodic
It looks like an amplitude scale placed at.

[0018] Since having a scanning grating 1 each three such regions B ₁ per graduation _period, B _2, B _3, acts as an amplitude grating under this point of view in the detection direction of each of the three lateral direction of diffraction . The ratio of the transparent area to the scale period is t =
It becomes 1/3. In the illustrated embodiment, each graduation period has three regions of equal width, so one 360 ° graduation period is divided into equal 120 ° components. This causes a phase shift of 120 ° in each of the three transverse diffraction directions between the signals obtained from different regions. Area B ₁
In the illustrated embodiment of the invention provides a 0 ° signal and regions B ₂ and B ₃ provide + 120 ° and −120 ° signals, respectively.

If one graduation period is divided into four regions of the same width, and these regions induce deflections of different angles in the direction of the associated detector, then four lateral deflection directions are similarly used. Two signals can be detected, each of which is 90 ° out of phase with each other. That is, it is possible to provide four regions having the same width D / 4. Two of these areas can be constructed in the same way as the _two areas B ₂ and B ₃ . To do this, place _two regions B ₂ 'and B ₃ ', offset by 180 ° with respect to the two regions, and these regions-
It is designed so that the deflection is one diffraction order.

In contrast to scanning gratings formed as phase gratings, in the amplitude scanning grating according to the invention the obtained longitudinal diffraction orders overlap in phase. Therefore, although one detector adds a large number of longitudinal diffraction orders, a sufficiently high degree of modulation can still be guaranteed. The graduation period of the scanned graduation plate can be selected relatively coarsely even if the focal length of the condenser lens is short.

In FIG. 5, the beam path in the described embodiment of the invention is shown once more schematically. In this case, the scanning grid 1 and the scale grid 2 can also only be partially recognized. When passing the scanning grating 1 for the first time, the beams b _1, b _2,
b ₃ is generated from the corresponding regions B _1, B _2, B ₃ of the scanning grating 1. After reflection and diffraction on the scale 2 of the measuring plate, the beams b ₂ and b ₃ are laterally patterned in areas B ₂ and B _3.
Is applied to the scanning grating 1 at positions spatially separated from each other. These positions are the beam b of the scanning grating 1.
_It is also spatially separated by the second point of incidence of ₁ . At different incident positions of the beams b _1, b _{2 and} b ₃ on the scanning grating 1, deflections in three different spatial directions are performed again. Therefore, the beam components reach the direction of the detector, these beam components pass through different areas B _1, B _2, B ₃ in the first pass and are different in the second pass of the scanning grating 1. The point is also deflected. In this case, it is not guaranteed that only the signal components of the desired phase angle will occur in each of the three detectors. Rather, it is an incoherent superposition of signal components of different phases such that phase separation at the detector is not possible.

That is, for example, complete signal loss occurs.
However, the three detectors are each 120 ° for evaluation.
Out-of-phase output signals, 0 ° signal, + 120 ° signal,
And-it is designed to output a 120 ° signal. Therefore, to ensure this, the interference signals b ₁ ′, b ₂ ′,
It is advantageous for the amplitude grating A to be superimposed on the scanning grating 1 in the Y direction so that only b ₃ ′ contributes to obtaining the scanning signal which occurs when it first passes through only one region of the scanning grating 1. In the drawing of FIG. 5, the amplitude grating A is chosen so that only the beam that emerges when it first passes through the transparent area B ₁ is detected. The partial beam shown in broken lines at the bottom of FIG. 5 is faded in with the amplitude grating A selected thereby. In this case, unlike the described embodiment, the amplitude structure can also be dimensioned so that only the signal components traveling through the second region when they first pass through the scanning grating eventually reach the detector. .

As can be seen from the embodiment of the scanning grating shown in FIG. 3, the amplitude structure orthogonal to the Y direction, that is, the measuring direction X, is similarly formed periodically. The area of the scanning grating labeled A is made opaque or absorptive so that only the partial beam deflected by the single direction-selective area reaches the detector when it first passes over the non-scan. Are arranged relative to each other.

The portion of the scanning grating 1 shown in FIG. 5 shows a diaphragm stripe A which adjoins only one stripe of the diffractive structure shown in FIG. In another configuration of the invention, the area B ₁
Is also formed laterally as a blazed grating, the parameters of which deviate from those of the gratings in regions B ₂ and B ₃ . Therefore, it is not necessarily compulsory to form one of the regions that act in a directionally selectable manner transparently, what is important is that different regions have different directional selectivity.

Furthermore, in order to optimize the imaging of the diffraction orders on the detector, the lattice constant of the region with the transverse grating varies laterally depending on the position. As a result, in addition to the illustrated embodiment, there are a series of other possibilities that make up the invention. It can be seen, for example, that the position measuring device according to the invention can also be realized in a transmitted light device. In this case, a first scanning grid, a scale grid, and other coalescing grids are provided. As a result, the scanning grating is formed according to the invention in this embodiment. That is, it is formed with the lateral structure having the direction selectivity described above.

[0026]

As explained above, the main advantage of the position-measuring device according to the invention is that the scanning signals which are out of phase with each other are generated in a simple way, in which case the diffraction orders obtained are Separation in the measuring direction) is no longer necessary. This guarantees the short focal length required for the imaging optics used. That is, a compact structure of the scanning head results.

Furthermore, with the aid of the position-measuring device according to the invention, it is possible in a (quasi) single-field scan to generate a position-dependent scanning signal which is insensitive to dirt on the scale plate and / or defective scale. Is advantageous. As a result, a relatively large tolerance is allowed in the scale of the scale plate, and it is possible to manufacture the plate in a cost-effective manner. In addition, the position measuring device according to the invention ensures a sufficient spacing insensitivity between the scale of the scale plate and the scale of the scanning plate.

[Brief description of drawings]

FIG. 1 is a schematic overall view of a position measuring device according to the present invention,

2 is a schematic beam path drawing of a position-measuring device used to generate interdependent signals for generating position-dependent signals, FIG.

FIG. 3 is a plan view showing a possible embodiment of the scanning grating of the position measuring device according to the invention,

FIG. 4 is a plan view showing a part of the scanning grating of FIG. 3;

FIG. 5 is a schematic view of the beam path inside the position measuring device of the present invention using the scanning gratings of FIGS. 3 and 4.

[Explanation of symbols]

1 Scanning grating 2 Scale plate grating B _1, B _2, B ₃ Patterned area in scanning grating d _1, d _2, d ₃ Lattice constant D _0, D _1, D ₂ detector b _1, b _2, b ₃ light beam bundle b ₁ ′, b ₂ ′ _, b ₃ ′ 0th transverse diffraction order, interference signal X measurement direction Y direction perpendicular to measurement direction X d scanning grating scale period L light source K collimator lens

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Valter Hoover, Federal Republic of Germany, 83278 Traunstein, Ettendorfer Wück, 6

Claims (12)

[Claims] 1. A measuring direction (X) having a constant scale period.
The light of the light source (L) is modulated according to the position by a plurality of gratings (1, 2) that move relative to each other, and the light beam bundles diffracted by at least one of the gratings interfere with each other and are out of phase with each other. A plurality of photodetectors (D _0, D _1, D ₂ ) for detecting position-dependent signals are provided, and at least one grating (1) is arranged in each of the scale periods (d) oriented in the measurement direction (X). At least three regions (B _1, which are sequentially arranged in the measurement direction (X) and extend substantially perpendicular to the measurement direction (X)) _.
B _2, B ₃ ), each of these regions (B _1, B _2, B ₃ ) has a different photoselective property, and these regions (B _1, B 3
Each of the signal beam bundles obtained from ( _2, B ₃ ) is incident on the attached photodetector (D _0, D _1, D ₂ ), and these photodetectors are almost in the measuring direction (X). A photoelectric position measuring device, which is arranged laterally. 2. Photoelectric position measuring device according to claim 1, characterized in that at least two regions (B _2, B ₃ ) are formed as a blazed phase grating and are oriented transversely to the measuring direction. . 3. At least two regions (B _2, B ₃ ) each form a phase grating oriented transversely to the measuring direction (X), the parameters of the grating being such that the zero diffraction order is suppressed. The photoelectric position measuring device according to claim 1, wherein the photoelectric position measuring device is selected. 4. A measurement is made within one graduation period (d) of the grating (1).
Three areas of the same width in a fixed direction (B_1,B_2,B_Three) Placed
Transparent areas (B₁) Also, the area
(B₂First photodetector for detecting the partial beam bundle from
(D₁) And the area (B_Three) From the partial beam bundle
First photodetector (D₂) And, both photodetectors (D
_1,D₂) Signals are 120 ° out of phase with each other and are transparent
Area (B ₁) From the third beam detector (D
₀) And the output signal of this detector is
It has the same phase shift of 120 ° with respect to
The photoelectric position according to any one of claims 1 to 3,
measuring device. 5. The photoelectric position measuring device according to claim 4, wherein the lattice constant of the lattice region is variable according to the position in a horizontal line with respect to the measuring direction. 6. Light from a light source is collimated and incident on a scanning grating having different regions by a lens, a scale plate grating is provided next to the scanning grating, and a partial beam bundle passing through this scale plate grating forms a united grating. Focusing on a plurality of photodetectors with another lens via, in which case a scanning grating is provided.
The photoelectric position measuring device according to claim 1, wherein the photoelectric position measuring device is formed according to any one of 1. 7. The light from the light source (L) is collimated by the lens (K).
Area (B _1,B_2,B_Three) With scanning grating
Incident on (1) and next to this scanning grating (1) a reflective eye
The plate grating (2) is installed, and the reflected partial beam bundle runs again.
Diffracted by a check grating (1) and a plurality of lenses by a lens (K)
Photodetector (D_0,D_1,D₂) Focus on and then scan
A grid is formed according to any one of the preceding claims 1-5
Photoelectric position measurement according to claim 1, characterized in that
apparatus. 8. Photoelectric position measurement according to claim 6 or 7, characterized in that the graduation plate grating (2) and the scanning grating (1) have the same graduation period (c = d) in the measuring direction (X). apparatus. 9. Photoelectric position measuring device according to claim 6 or 7, characterized in that the scale plate grating (2) is a phase grating. 10. The scanning grating (1) is characterized in that it has a diaphragm-like amplitude structure (A) oriented transversely to the scanning direction (X) in order to shield unwanted signal components. The photoelectric position measuring device according to claim 1. 11. The amplitude structure (A) is capable of detecting on the detector side only the signal component (b ₁ ) in which the incident beam bundle passes through only one region (B ₁ ) at the first passage, but other Photoelectric position measuring device according to claim 10, characterized in that it is arranged to block the signal components (b _2, b ₃ ) passing through the regions (B _2, B ₃ ). 12. The photoelectric position measuring device according to claim 2, wherein the entire region is formed as a blazed phase grating within one graduation period and is oriented laterally with respect to the measuring direction.